We propose to adapt and implement dual-diagnosis motivational interviewing (DDMI) and integrated group therapy (IGT) to evaluate the feasibility of a jail-to-community treatment continuum for adults with co- occurring substance use and mental disorders (CODs). More than 2 million adults with serious mental illnesses are admitted to jails annually and approximately three-quarters of them have substance use problems. Although improvements have been made in treating CODs in inpatient and outpatient settings, there remains a gap in the science and practice of treating jail inmates with CODs. Too few receive integrated in-custody and in-community evidence-based treatments that focus on community reentry and criminogenic risk. Achieving sustained community tenure for jail inmates with CODs requires adapting existing evidence-based practices. DDMI and IGT have strong evidence bases and represent appropriate adaptation candidates. Thus, a rigorous study is needed to evaluate the feasibility and acceptability of adapting and integrating these programs across jail and community settings. Guided by the risk-need- responsivity model and the Evidence-Based Interagency Implementation Model, we propose two sequential aims: Aim 1: To adapt DDMI and IGT for delivery to jail inmates, examining the initial acceptability of the adaptations through an uncontrolled open trial (N=12), and Aim 2: To conduct a randomized trial (N=60) to establish knowledge in three areas: Aim 2.1: The feasibility and acceptability of the adapted DDMI and IGT; Aim 2.2: The feasibility and acceptability of the proposed research and communication protocols; and Aim 2.3: The effectiveness of and estimated effect sizes associated with the adapted interventions vis-a-vis reductions in substance use, psychiatric symptoms, and re-arrest and improvements in uptake of usual care. We will use an iterative approach to adapt the programs, including consultation with experts and community providers. Our uncontrolled trial will inform subsequent treatment, research, and communication protocol refinements prior to our randomized trial with assignment to treatment condition (i.e., continuum of DDMI-IGT and usual care vs. usual care only). Our application builds in part on our study team's NIH-funded grants and successful collaborations in prevention and treatment of drug and alcohol use and mental health symptoms, the provision of clinical services to jail inmates with CODs, and the adaptation and implementation of clinical treatment programs. Our proposed R34 will complement professional standards calling for evidence-based treatments for adults with CODs. These efforts will improve the field's understanding of the nexus of CODs and arrest and help improve multiple outcomes, including reductions in substance use, mental health symptoms, and justice involvement, and uptake of usual care, all of which will be evaluated in a follow-up R01.